Natural diet? Is this the food that you are referring to?
http://www.kensfish.com/aquarium-supplies/fish-food-feeders/kens-premium-krill-pellet-40-mm.html
If so, the ingredients are no more natural than Massivore, and while I don't debate the results that you had with Massivore, a result such as that with a single pair of fish becomes purely anecdotal evidence in the grand scheme of things.
But here's the thing, the krill pellets from Ken appear to be designed more for a high energy cold water fish such as salmon/trout, not warm water tropical fish that live in a small glass cage.
Guaranteed analysis: protein 45%; fat 24%; fiber 3%
24% crude fat is WAY TOO MUCH fat for
any tropical fish. It may have triggered your fish to spawn, but over time it will cause health issues in your fish if fed as the staple, especially for anyone who tends to overfeed their fish.
Fat is primarily utilized by fish as an energy source, so the amount required for optimum health will vary within species, as well as the life stage of the fish. The higher the metabolic rate of the fish, the more fat that will be required by the fish. Generally speaking, the vast majority of tropical species will function best on a diet that contains less than 10% crude fat.
An Evaluation of Two Commercially Prepared Feeds on Growth Performance and Liver Condition of Juvenile African Cichlids Pseudotropheus socolofi and Haplochromis ahli
North American Journal of Aquaculture
Volume 66, Issue 4, 2004
http://www.tandfonline.com/doi/abs/10.1577/A03-035.1
The problem with fatty deposition of the liver is you can't see it with the naked eye, it can build up very quickly, and if not corrected can shave years off of the life of an otherwise healthy specimen.
Also from this study ....
This had nothing to do with massive overfeeding, or fish that appeared obese. Without performing a necropsy, and examining the histological changes in the liver under a microscope, the average hobbyist wouldn't have clue one as to the potential long term damage they were doing to their fish.
The fish used in this study were only 4 weeks old when the feed trial began, and averaged 0.06 g in weight, and 1.5 cm in total length.
Now imagine what happens to the liver of an adult CA/SA cichlid (with much lower metabolisms) when fed diets that contain excessive amounts of lipids. (fat)
The juvie H. ahli (actually an S. fryeri) used in this study fared much better being a carnivore, but it still showed a lipid accumulation in the hepatocytes. (<50%) The P. socolofi had extensive lipid accumulation when fed the TP diet.
This study came about after some cichlid farms in south FL suffered from some large mortalities in both 1998 & 1999. When the dead fish were examined they showed fatty infiltration of the liver, heavy vacuolation, and severe necrosis of the liver, pancreas, and spleen.
It was suggested to the farms that they replace ther feeds with one that had a lower lipid content (less than 10%) and supplement the feed with a vitamin premix. Clinical signs in the affected farms were resolved after implementation of these recommendations.
